1. Technical Field
The present invention relates to medical devices, systems and methods. More particularly, the present invention relates to devices, systems and methods for preventing the embolic material from entering carotid arteries that supply blood to the brain.
2. Background Information
Cerebrovascular diseases are considered among the leading causes of mortality and morbidity in the modern age. Strokes denote an abrupt impairment of brain function caused by pathologic changes occurring in blood vessels. The main cause of strokes is insufficient blood flow to the brain (i.e., ischemic stroke), which accounts for about 80% of stroke cases.
Ischemic strokes are generally caused by a sudden occlusion of an artery supplying the blood to the brain. Total occlusions or partial occlusions (i.e., stenosis) are often the result of diseases of the arterial wall. Arterial atherosclerosis is by far the most common arterial disorder, and when complicated by thrombosis or embolism it often is the most frequent cause of cerebral ischemia and infarction, resulting in cerebral stroke.
Cardioembolism causes about 15-20% of all strokes. Stroke caused by heart disease is primarily due to embolism of thrombotic material forming on the atrial or ventricular wall or the left heart valves. These thrombi can then detach and embolize into the arterial circulation. Emboli large enough can occlude large arteries in the brain territory and cause strokes.
Cardiogenic cerebral embolism is presumed to have occurred when cardiac arrhythmia or structural abnormalities are found or known to be present. The most common causes of cardioembolic stroke are nonrheumatic (non-valvular) atrial fibrillation (AF), prosthetic valves, rheumatic heart disease (RHD), ischemic cardiomyopathy, congestive heart failure, myocardial infarction, post-operatory state and protruding aortic arch atheroma (A.A.A.).
Such disorders may be treated in various ways. For example, the disorders may be treated by drug management, surgery (carotid endarterectormy) in case of occlusive disease, and or carotid angioplasty and carotid stents.
While endarterectomy, angioplasty and carotid stenting are procedures targeted at opening the occluded artery, they do not prevent progression of new plaque. Even more so, the above treatment methods only provide a solution to localized problems and do not prevent proximal embolic sources, i.e., embolus formed at remote sites (heart and ascending aorta) to pass through the reopened stenosis in the carotid and occlude smaller arteries in the brain. This is a substantial problem, inasmuch as about one-third of patients suffering from carotid occlusion also have proximal embolic sources leading to stroke. It should be noted that only about 20% of the cases of stroke result from an occlusion of the carotid arteries.
It will also be appreciated that endarterectomy is not suitable for intracranial arteries or in the vertebrobasilar system since these arteries are positioned within unacceptable environment (brain tissue, bone tissue) or are too small in diameter.
Introducing filtering means into blood vessels, in particular into veins, has been known for some time. However, filtering devices known in the art are generally of a complex design, which renders such devices unsuitable for implantation within branchiocephalic and or carotid arteries, and unsuitable for handling fine embolic material. Also, the filtering devices known in the art often become clogged and need to be cleaned or replaced. However, when considering the possible cerebral effects of even fine embolic material occluding an artery supplying blood to the brain, the consequences may be fatal or may cause irreversible brain damage.
In light of the short period of time during which brain tissue can survive without blood supply, there is significant importance to constantly providing suitable means for preventing even small embolic material from entering the carotid arteries, so as to avoid stroke and brain damage.
U.S. Pub. No. 2004/0167613 describes implantable devices for positioning about a blood vessel bifurcation zone to control flow of embolic material around the bifurcation. This device includes an anchoring element extending within the zone of bifurcation to anchor the device therein, and a deflecting element, associated with the anchoring element. The deflecting element includes a mesh having a mesh size sufficient to allow passage of blood without hindrance whilst preventing the passage of embolic material exceeding a predetermined size.
U.S. Pub. No. 2006/0161241 A1 discuses methods for treating mobile aortic atheroma, the method includes providing a radially expanding stent-like device and deploying distal protection device(s), such as a filter.
The left atrial appendage (LAA) is one of the most frequent sources of cardiogenic thrombi in patients with atrial fibrillation. There are two devices that are used for closing LAA from circulation and to prevent cardioembolic events: the Percutaneous Left Atrial Appendage Transcatheter Occlusion (PLAATO™) system (ev3 Inc., Plymouth, Minn., USA) and the WATCHMAN® filter system (Atritech Inc., Plymouth, Minn., USA).
Nakai et al. (Nakai et al., Circulation, 105:2217-2222 (2004) describe the PLAATO™ device, which is a LAA occlusion system that consists of an implant and a delivery catheter. The implant is composed of a nitinol metal cage with multiple struts that are outwardly bent. The device includes an occlusive membrane of expanded polytetrafluoroethylene (ePTFE), which is laminated directly to the frame, and is supported so that the perimeter has intimate contact with the inner wall of the appendage.
Bayard Y et al. (Bayard Y et al., Expert Rev of Cardiovascular Therapy, 3(6):1003-1008 (2005)) describe the PLAATO™ and the WATCHMAN® devices. The WATCHMAN® filter system consists of a nitinol framework and it is covered with a thin permeable polyester membrane with pores.
U.S. Pat. Pub. 2007/0060994 describes a blood flow diverter device for treatment of intracranial aneurysms, including a porous tubular member having a central portion and two ends.
As previously discussed, a significant drawback of some of the known filtering means is their tendency to become clogged. These devices need to be either cleaned or replaced to avoid significant patient complications.
As such, there is need to provide self cleaning devices, systems and methods for preventing embolic material from entering the carotid arteries supplying blood to the brain, and thus preventing emboli from occluding small intercranial arteries in the brain and preventing strokes. It would be advantageous if such devices were suitable for permanent implantation.